How does a refrigerator work?
Date: Around 1993
How does a refrigerator work?
Most common refrigerators have four major parts to its
refrigeration system -- a compressor, condenser, expansion valve, and
evaporator. In the evaporator section, a refrigerant (up until very recently
it has been "DuPont's Freon (TM)-12", or dichlorodifluoromethane) is vaporized, and heat is
absorbed through the inside walls of the refrigerator, making it cold inside.
DuPont's Freon (TM)-12 boils at -6.6 C (about 20 F) when pressurized at 35.7 pounds per
square inch, so evaporator temperature is maintained at or near that
temperature if the refrigerator is working properly. In the next stage, an
electric motor runs a small piston or Wankel compressor (some new compressors
are vane type) and the DuPont's Freon (TM)-12 is pressurized. That raises the temperature
of the DuPont's Freon (TM)-12. The resulting super-- heated, high-pressure gas (it is
still a gas at this point) is then condensed to a liquid in an air-cooled
condenser. On most refrigerators, the compressor is on the bottom and the
condenser coils are on the rear of the refrigerator. From the condenser, the
liquid DuPont's Freon (TM)-12 flows through an expansion valve, in which its pressure and
temperature are reduced the conditions that are maintained in the evaporator.
The whole process operated continuously, by transferring heat from the
evaporator section (inside the refrigerator, to the condenser section (outside
the refrigerator), by pumping the DuPont's Freon (TM)-12 continuously through the system
described above. When the desired temperature is reached, the pump stops and
so does the heat transfer. Freezers and air conditioners work exactly the
same way. The difference is mostly in their compressor capacities and
differing pressures. For example, to maintain -20 F (-29 C), as with a frozen
food freezer, DuPont's Freon (TM)-12 must maintain a pressure of 15.3 pounds per square inch
in the evaporator section. Because of the concerns regarding
chlorofluorocarbons in the past several years, new refrigerators do not use
DuPont's Freon (TM)-12 any more. In fact, in years gone by (I will show my age here),
refrigerators used Ammonia as a refrigerant! New materials to replace DuPont's Freon (TM)-
12 have been developed, and are currently being developed. Now to totally
confuse you, there are some refrigerators that use the absorption system of
heat transfer. These refrigerators are operated usually by natural or LP gas.
In these refrigerators a strong solution of ammonia in water is heated by a
gas flame in a container called a generator, and the ammonia is driven off as
a vapor. The ammonia vapor then goes into a condenser, where it is changed to
its liquid state. The ammonia then flows into the evaporator, just like a
conventional system. But, instead of the gas being brought into a compressor
after leaving the evaporator, the ammonia gas is reabsorbed in the partially
cooled, weak solution returning from the generator, making it a strong ammonia
solution, again. This process happens in another small container called, you
guessed it, the absorber. From there this concentrated solution flows back to
the generator to complete the cycle. This is the type of refrigerator that is
seen most often in campers and RV's.
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Update: June 2012